1. Field of the Invention
Embodiments of the present invention relate in general to a system for the monitoring of AC power sources and loads. More specifically, the present invention relates to a self-contained, in-line electrical plug for monitoring/storing data relating to source and load use or abuse for electric tools and appliances, for later transfer and analysis of the data.
As an introduction to the problems solved by the present invention, it is desirable for various reasons to know the status of an AC power source or of a piece of equipment that is connected as a load to an AC power source. Numerous power-monitoring inventions are available which connect externally between the power source and load. However, none of the monitoring inventions that are known to exist have the features of the present invention. The AC power monitoring device of the present invention is unique in that the entire electronic circuit is self-contained within a universal AC plug body, being of any type of conventional plug used for 115 volt, 230 volt or other AC voltages. It will become clear from the descriptions that follow that this invention is useful and novel.
2. Related Art
The inventor has identified several prior art references in the U.S. patent art. U.S. Pat. No. 4,652,139 by Sulcer describes a non-volatile elapsed-time meter. U.S. Pat. No. 4,920,549 by Dinovo describes a means for collecting data about the accumulated run-time and average cycle-time of a switched circuit, typically for tracking equipment run-time. These devices do not record voltage spikes, surges, brief dropouts or other perturbations of the supply line. These devices only record the accumulated time that a supply of power was detected as being present. In addition, Dinovo""s invention also calculates and stores the average on-time of a piece of equipment.
U.S. Pat. No. 5,315,236 by Lee is a monitor that measures the instantaneous power and total accumulated energy consumed by a device. It is a device that plugs into an electric socket and has a separate receptacle for an appliance plug. Lee""s invention is dissimilar to the present invention in that the device is not built into a plug-body and it lacks certain monitoring capabilities that are incorporated into the present invention.
Still, there is a need for a convenient, compact in-line plug that can be used to monitor total usage of equipment such as a tool/appliance as well as the details of use or abuse of the equipment. An in-line plug is needed that can be supplied along with, for example, rented equipment to allow the owner of the equipment to plan maintenance or replacement. Such a plug is needed to allow the equipment owner to know the treatment of his equipment away from his possession, for improved budgeting, billing, maintenance supervision, etc.
Accordingly, in the present invention, an electronic circuit is assembled onto a miniature printed circuit board and assembled into an AC plug body such that the AC mains connect to terminals on or connected to the printed circuit board. The circuit contains a filtered power supply, microcontroller, and external interface, such that the plug may be connected to a special interface connector in order for data to be exchanged with a PC or computer or other programmer/reader device. The reader or PC interface also allows for erasure of a non-volatile EEPROM and for networking of several plug devices to a central reader which facilitates the networking of appliances. A current sensor is employed, preferably a differential type sensor such as a differential Hall Effect sensor. Alternatively, other current sensors may also be used, such as a magnetic pick-up (clamp) device with current sensing inductors that are located such that they are parallel to the two power leads. The inductors may form a differential current sensor which is immune to electromagnetic noise. Or, a low resistance connected in series in the hot or neutral line, with measurement of voltage across the resistance, may also be used. A voltage sensor is also employed. From the combined readings from the voltage sensors and the current sensor, the embedded program running on the microcontroller can determine the power being consumed by the loading device.
In one embodiment of the invention, the circuit contains a real-time clock and RAM memory, both of which are powered by a back-up battery. With these features, it is possible to store real-time information, such as the occurrence of peak loads or voltage spikes, for example. Information regarding the intensity and duration of other undesirable or anomolous events, both elapsed-time and real-time, can be time-stamped and stored in the battery-backed RAM memory.
In another embodiment, non-volatile memory, such as EEPROM memory, may be used without the need of a battery. Such an embodiment would not be capable of affixing real-time time-stamps to detected events, but only elapsed time-stamps, beginning when the equipment being monitored was plugged-in for that particular period of use.
In another embodiment, the invention incorporates a ground-fault detection circuit, such that hazardous or undesirable ground currents will cause a circuit interrupter to trip, disconnecting the load from the power source and preventing damage to equipment or electric shock. A fault test push-button switch and a fault reset push-button switch enable the user to test and/or reset the circuit interrupting device.
These and other embodiments, aspects, advantages and features of the present invention will be set forth in part in the description, and in part will come to be understood by those skilled in the art by reference to the following description of the invention and referenced drawings, or by practice of the invention.